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Regulation of Gene Expression You Must Know • The functions of the three parts of an operon. • The role of repressor genes in operons. • The impact of DNA methylation and histone acetylation on gene expression. • The role of oncogenes, proto-oncogenes, and tumor suppressor genes in cancer. Bacteria respond to environmental change by regulating Transcription. • Genes are clustered into units called operons. • 3 parts of an operon: – Operator- controls the access of RNA polymerase to the genes. – Promoter-where the RNA polymerase attaches. – Genes- The entire stretch of DNA required for al the enzymes produced by the operon. General structure of an OPERON Regulatory Genes • Produce repressor proteins that may bind to the operator site. • When they occupy the operator site, RNA polymerase is blocked from the genes of the operon. • This means the operon is off. Repressible Operon • Is normally on but can be inhibited. • Is Anabolic, building an organic molecule. • The repressor protein produced by the regulatory gene is inactive. • If the organic molecule that is produced is provided to the cell, the molecule can act as a corepressor and bind to the repressor protein, activating it. Inducible Operon • Normally off, but can be operated. • Normally catabolic, breaking down food molecules for energy. • To turn the inducible operon on, an inducer binds to and inactivates the repressor protein. • Now RNA polymerase can access the genes of the operon. Regulation of Genes • The expression of Eukaryotic genes can be turned off and on at any point along the path to becoming a protein. • Different cell types are due to differential gene expression, the expression of different genes by cells with the same genome. Packaging of DNA • A nucleosome is a packaging unit of DNA. – Consists of DNA bound ot small proteins called histones. – The more tightly bound DNA is to its histones, the less accessible it is for transcription. – This relationship is governed by 2 chemical reactions. • DNA methylation- the addition of Methyl groups to DNA – Causes DNA to become more tightly packaged, thus reducing gene expression. – Histone acetylation- acetyl groups are added to amino acids of histone proteins, making the chromatin less tightly packaged, encouraging transcription. Recap • Methylation- occurs on DNA & reduces gene expression • Acetylation- occurs on histones & increases gene expression Other factors of Gene expression • Transcription initiation is another important control point in gene expression. • The control of gene expression may also occur prior to translation and just after translation, where proteins are processed. Connection to real life • Cardiovascular disease – Gene expression provides valuable, tissue and cell-specific information about the molecular mechanisms involved in disease processes, allowing a clinician to, for example, evaluate cardiovascular disease state, activity, and/or progression at a point in time. Links • http://web.mit.edu/bioedgroup/animations. htm A program of differential gene expression leads to the different cell types in a Multicellular organism. • Zygote undergoes transformation through three interrelated processes. – Cell division – Cell differentiation- cells specialize – Morphogenesis- organization of cells into tissues and organs. What controls differentiation & Morphogenesis? • Cytoplasmic Determinants – Maternal substances in the egg that influence the course of the early development. – They are unevenly distributed in the early cells of the embryo and result in different effects. • Cell-cell signals – Results from molecules, such as growth factors produced by one cell influencing neighboring cells, a process called induction which causes cells to differentiate. – Determination • Series of events that lead to observable differentiation of a cell. • Differentiation is caused by cell-cell signals and is irreversible. – Pattern Formation • Sets up the body plan and is a result of cytoplasmic determinants and inductive signals. • Determines head and tail, left and right, back and front. • Uneven distribution of morphogens plays a role in establishing these axes. • Stem Cell Animation Cancer Results from genetic changes that affect cell cycle control. • Oncogenes- are cancer-causing genes. • Proto-oncogenes- genes that code for proteins that are responsible for normal cell growth. – Become oncogenes when a mutation occurs that causes an increase in the product of the protooncogene, Or – an increase in the activity of each protein molecule produced by the gene. • Cancer can be caused by a mutation in a gene whose products normally inhibit cell division. – These genes are called tumor-suppressor genes. • Cancer development is based on the idea that cancer results from the accumulation of mutations that occur throughout life. – The longer we live, the more mutations that are accumulated and the more likely that cancer might develop. Activities • This weeks CAR: • What does Stem cell Research Mean to you? – Different types of Stem Cells? – How are they cultured in the lab? – What are some issues in Stem cell research? – What are some issues that you have?